It is examined to apply the High-Speed Uplink Packet Access (HSUPA) to a mobile communication system of the Wideband-Code Division Multiple Access (W-CDMA) method in order to improve communication speed. The HSUPA is a function of providing an access in an uplink direction of a larger band (direction from a terminal to a network) in a mobile communication system.
In the following, after explanation of outline of a conventional mobile communication system, a protocol model of the HSUPA will be described. FIG. 16 is a diagram illustrating the configuration of a conventional mobile communication system. As illustrated in the diagram, the mobile communication system has a mobile terminal (UE) 10, basestations (Node B) 20 to 22, Radio Network Controllers (RNCs) 30 and 31, and a Core Network (CN) 40.
The intervals between the CN 40, the RNCs 30 and 31 and the basestations 20 and 21 are wires intervals, and intervals between the basestations 20 to 22 and the mobile terminal 10 are wireless intervals. The interface between the mobile terminal and the basestation is called Uu, the interface between the RNC and the basestation is called Iub, the interface between the RNC and the RNC is called Iur, and the interface between the CN and the RNC is called Iu.
In the mobile communication system of FIG. 16, when user data is received by the mobile terminal 10, the user data is transmitted to the RNC 30 accommodating the mobile terminal 10 via the CN 40. When the mobile terminal 10 presents in a cell 1, the RNC 30 transmits the user data to the basestation 20 accommodating the cell 1, and the basestation 20 transmits the user data to the mobile terminal. On the other hand, the user data transmitted from the mobile terminal 10 is received by any of the basestations 20 to 22, transmitted to the RNCs 30 and 31, and transmitted to the destination via the CN 40.
FIG. 17 is a diagram for explaining a protocol model of the HSUPA, and FIG. 18 is a diagram illustrating outline of data communication (Iub/Iur boundary). As illustrated in FIG. 17, a mobile terminal has layers of Application (APL), Radio Link Control (RLC; regarding RLC, refer to 3GPP TS25.322), Medium Access Control (MAC)-d, MAC-es, MAC-e, and physical layer (PHY), and a basestation has layers of MAC-e/Enhanced Dedicated Channel (EDCH) Frame Packet (FP) and PHY/TNL.
The RNC has a D-RNL (relay device) and an S-RNC. The D-RNC has a layer TNL/TNL, and the S-RNC has layers APL, RLC, MAC-d, MAC-es, EDCH FP, and TNL.
A data frame transmitted in the network direction (uplink direction) by the mobile terminal is divided in short Packet Data Unit (PDU) by the function of the PLD/MAC-es layer. After that, some MAC-d PDUs are multiplexed, there by constructing an MAC-es PDU (refer to the first to third stages in FIG. 18).
To the MAC-es PDU, a TSN as sequence number is given. In the HSUPA, by simultaneously performing the HARQ in a plurality of channels, the communication rate is improved. However, it is uncertain that data of which channel is received first. Consequently, the order of data received by the basestation is not assured. Due to this, when the mobile terminal transmits data frames, sequence numbers (TSN) are given on the MAC-es unit basis and, to assure order in the RNC, re-ordering is performed according to the TSNs.
Some more MAC-es PDUs are further multiplexed at the time of transmission from the basestation to an S-RNC and transmitted on the EDCH FP unit basis (EDCH FP frame) onto the Iub. Also to the EDCH FP frame, the FSN as a sequence number is given (refer to the fourth stage in FIG. 18).
FIG. 19 is a diagram illustrating an example of the data structure of the EDCH FP frame. As illustrated in the diagram, the EDCH FP frame has header and payload, and the header has various control information (not illustrated) and the FSN. The payload has a plurality of Mac-es PDUs, and each MAC-es PDU has a TSN.
On the other hand, on the S-RNC, the MAC-es PDU is extracted from the received EDCH FP frame, re-ordering is performed in accordance with the TSNs and, further, a process of reproducing a data frame is performed by terminating the MAC-d/RLC layer.
As described above, transmission on the Iub/Iur is performed on the EDCH FP unit basis. Consequently, when a cause of frame drop such as congestion of a line occurs on the Iub/Iur, the unit of the drop also becomes the EDCH FP unit.
Therefore, in the case where drop occurs on the Iub/Iur, it is repaired by retransmission by the RLC between the mobile terminal and the RNC. In a standard mobile communication system, the S-RNC has the function of detecting the drop by monitoring the FSN of the EDCH FP received, when drop is detected, regarding it as line congestion in the Iub/Iub, and notifies the basestation of the congestion indication (TNL congestion indication). The basestation which receives the congestion notification from the RNC side has the function of suppressing data transmission to the Iub/Iur by a predetermined amount or a predetermined period.
Japanese Laid-open Patent Publication No. 2006-86989 discloses a technique of improving throughput by waiting for an uplink retransmission packet only for predetermined time, transmitting a retransmission wait cancelling request to a wireless network control apparatus and, in the case where a retransmission wait cancellation response of instructing stop of retransmission waiting is received from the wireless network control apparatus, stopping the retransmission waiting.
However, in the case where a frame related to uplink traffic of the mobile communication system drops on the Iub/Iur, data communication has to be executed again between the RNC and the mobile terminal. Consequently, the conventional technique has a problem such that the band of the limited wireless interval is wasted.
In the case where the HSUPA is newly introduced in the form of expanding an existing W-CDMA system which is already operating, it is not easy to sufficiently assure the band of the Iub/Iur in relation with the existing system. The problem becomes more serious.